A shape detection device is arranged between stands of a multistage rolling mill. To synchronize rolling speeds of the stands, a rolling material is threaded on rolls which are rotatably supported and the rolls are oscillated in upper and lower directions, so that the rolling material can have a loop to apply a certain tension. Then, a plate shape (plate thickness) of the rolling material is computed on the basis of the detected tension distribution in the width direction of the rolling material to control the roller. With this, the shape in the width direction of the rolling material can be uniform, so that edge waves, intermediate elongation, and the like can be prevented.
Such a conventional shape detection device is disclosed in Patent Documents 1 to 4.    Patent Document 1: Japanese Patent Application Laid-open No. Hei10-314821    Patent Document 2: Japanese Patent Translation Publication No. 2003-504211    Patent Document 3: Japanese Examined Patent Publication No. Hei5-86290    Patent Document 4: Japanese Patent Application Laid-open No. 2004-309142